microblaze: support gpio_to_irq()
microblaze: support gpio_to_irq()

gpiolib returns -ENXIO if struct gpio_chip::to_irq isn't set, so it's
safe to always call.

Based on PPC patch
"powerpc/gpio: support gpio_to_irq()"
78331aded913d76c7ff996a1a0747d54b057460b

Signed-off-by: Michal Simek <3a191dd2be46e826fee926d532b136ed65cb5318@monstr.eu>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas